package io.neural.micro;

/**
 * 基于Twitter的分布式自增ID算法Snowflake实现分布式有序
 * 
 * @author lry
 */
public class Snowflake {

	private final long twepoch = 1288834974657L;// 起始标记点，作为基准
	private final long workerIdBits = 5L;//只允许workid的范围为：0-1023
	private final long datacenterIdBits = 5L;
	private final long maxWorkerId = -1L ^ (-1L << workerIdBits);
	private final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
	private final long sequenceBits = 12L;
	private final long workerIdShift = sequenceBits;
	private final long datacenterIdShift = sequenceBits + workerIdBits;
	private final long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
	private final long sequenceMask = -1L ^ (-1L << sequenceBits);

	private long workerId;
	private long datacenterId;
	private long sequence = 0L;
	private long lastTimestamp = -1L;

	public void init(long workerId, long datacenterId) {
		if (workerId > maxWorkerId || workerId < 0) {
			throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
		}
		if (datacenterId > maxDatacenterId || datacenterId < 0) {
			throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
		}
		
		this.workerId = workerId;
		this.datacenterId = datacenterId;
	}
	
	public Long nextLong() {
		return this.nextId();
	}

	public String next() {
		return String.valueOf(this.nextLong());
	}
	
	public synchronized Long nextId() {
		long timestamp = timeGen();
		if (timestamp < lastTimestamp) {//闰秒
			long offset = lastTimestamp - timestamp;
			if (offset <= 5) {
				try {
					wait(offset << 1);
					timestamp = timeGen();
					if (timestamp < lastTimestamp) {
						throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", offset)); 
					}
				} catch (Exception e) {
					throw new RuntimeException(e);
				}
			} else {
				throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", offset));
			}
		}
		
		if (lastTimestamp == timestamp) {
			sequence = (sequence + 1) & sequenceMask;
			if (sequence == 0) {
				timestamp = tilNextMillis(lastTimestamp);
			}
		} else {
			sequence = 0L;
		}

		lastTimestamp = timestamp;

		return ((timestamp - twepoch) << timestampLeftShift) | (datacenterId << datacenterIdShift) | (workerId << workerIdShift) | sequence;
	}

	/**
     * 保证返回的毫秒数在参数之后
     * 
     * @param lastTimestamp
     * @return
     */
	protected long tilNextMillis(long lastTimestamp) {
		long timestamp = timeGen();
		while (timestamp <= lastTimestamp) {
			timestamp = timeGen();
		}
		return timestamp;
	}

	/**
     * 获得系统当前毫秒数
     * 
     * @return
     */
	protected long timeGen() {
		return System.currentTimeMillis();
	}

}
